The present disclosure relates generally to an apparatus for bilateral imaging of a first and a second breast of a person, and particularly to an arrangement of RF coils for simultaneous bilateral imaging.
Magnetic resonance imaging (MRI) mammography is useful in assessing the size of a tumor for surgical planning, especially with difficult histology such as infiltrating lobular carcinomas and extensive intraductal components. It has also shown to be accurate in the staging of cancers as well as determining the amount of chest wall or pectoralis invasion. Screening of the opposite breast of interest may be important in cases where a patient has a form of disease with high probability of bilaterality, for example, invasive lobular carcinoma, as well as assessing patients for contralateral breast disease. Assessment of the contrast uptake dynamics through MR imaging has been found to increase specificity and change clinical treatment in many cases.
An MRI system uses a static magnetic field B0 to align magnetic spins in the direction of the field, usually denoted along the z-axis. A rotating RF field B1 applied perpendicular to the B0 field will cause the spins to rotate into the transverse field at a resonant frequency. The transverse component of the magnetization can be detected through the use of an RF antenna or receiver coil, which is specifically tuned to the resonate frequency of the precessing spins, otherwise know as the Larmor frequency. The signal-to-noise-ratio (SNR) of the system is dependent on the filling factor of this RF coil, resulting in local RF coils being used to increase the SNR of the system. With RF coils, it is desirable to both optimize the SNR of the system and provide a comfortable environment for the patient, thus decreasing patient movement during the scan. It is also desirable to provide a coil that allows for optimal patient placement during the scan in order to minimize artifacts from the system.
With some MRI techniques, there may be trade-offs between spatial resolution and acquisition time, that is, using a low resolution imaging technique and acquiring many temporal time points versus using a mode of high resolution imaging and acquiring few temporal time points. For bilateral breast imaging acquisition, several methods have been used to produce dynamic enhancement parametric curves. The use of axial and coronal slices is commonly used but may reduce the acquisition efficiency and spatial resolution of the image. The axial volumes may be acquired with a significant amount of zero-filling in k-space in order to keep the acquisition times reasonable. However, for these interpolated data sets, the real spatial resolution of the images may not be equal to the reconstructed voxel size. A second imaging method is to toggle back and forth between the left and right breast volumes, thereby maintaining the spatial resolution but possibly effecting the temporal resolution and decreasing the efficacy of the enhancement curve. A third imaging method is to perform the imaging of the left and right breasts on separate days, which may be inconvenient for the patient.
An alternative imaging method is to use parallel imaging in the slice direction using a multi-element array coil where individual RF coil elements are more sensitive to one of the breast volumes than to the other. From the resultant data, a signal processing parallel imaging technique may be used to acquire sagittal slices from both breasts simultaneously. Here, a single large volume encompassing both left and right breasts is prescribed such that a volume V′ is aliased back into a volume V. To unalias the volume data into slices corresponding to volumes V and V′, the coil element sensitivities are used by the signal processing parallel imaging technique.
To advance the field of MRI mammography, there remains a need in the art to separate coil sensitivity maps in the encoding direction, thereby enabling higher temporal resolution and higher spatial resolution.